High-carbon ferromanganese process



United States Patent 3 083 692 HIGI-XM9N FERiQOh dANGANESE FROCESS August M. Isuhlrnann, Niagara Falls, N.Y., assignor to graph Qarbide Corporation, a corporation of New our No Drawing. Filed Dec. 27, 1960, Ser. No. 78,256 3 Claims. (Cl. TS-=51) The present invention relates to an improved metallurgical process for the production of highwarbon ferromanganese alloys.

High-carbon ferromanganese, also known in the metal lurgical field as standard ferromanganese, is the most commonly used means of adding manganese to steel for the purpose of alloying or deoxidizing and cleansing.

High-carbon ferromanganese contains approximately 74 to 76 percent by weight of manganese, up to about 1 percent by weight of silicon, about 7 percent by weight of carbon, and the balance substantially iron and incidental impurities.

A common method for preparing this high-carbon ferromanganese comprises the smelting of an oxidic manganese ore with a basic flux. A considerable quantity of manganese is, however, lost during this operation because of excessive volatilization of the manganese owing to the elevated temperatures employed in the process. The smelting temperature must be quite elevated in order to maintain the slag in a state of sufiicient fluidity; since the slag is usually highly basic, a considerable degree of refractoriness ensues, which, among other things, facilitates the volatilization of the manganese in the melt. The high basicity of the slag is due mainly to the large amounts of calcium and, or magnesium oxides added to the melt to keep the manganese oxide content of the slag as low as possible. While a highly basic slag, derived from such additions of calcium and/ or magnesium oxides, prevents uneconomical losses of manganese metal to the slag, it contributes considerably to the large losses of manganese metal to the stack, thus defeating its purpose. Commercial practice is, therefore, at best a compromise between these two alternatives.

it is, accordingly, an object of the present invention to provide an improved process for producing highcarbon ferromanganese without substantial losses of manganese.

These and other objects and advantages of the present invention will be apparent from the following detailed description and from the appended claims.

Briefly stated, the subject invention provides an improved process of producing high-carbon ferromanganese which comprises preparing in a smelting furnace an intermediate high-carbon alloy containing from about 2 to about percent by weight of silicon, and a slag possessing a base-to-acid ratio not greater than about 1.7; separating the intermediate alloy so produced from the slag and treating the separated intermediate alloy in a desiliconizing vessel with a manganiferous oxidizing agent and an oxygen-containing carrier gas to desiliconize this alloy from the original 2 to 5 percent by weight silicon to a silicon content not greater than 1 percent by weight and to form a manganese-bearing slag. This manganese-bearing slag can be recycled to tl e smelting furnace for reemployment.

The intermediate high-carbon alloy containing from about 2 to about 5 percent by weight of silicon may be prepared in any suitable smelting electric furnace, such as a single or two-electrode, single phase, submerged arc furnace or a three-electrode, three-phase, submerged arc furnace, by reacting manganese ore with a basic fiuxing agent and a carbonaceous reducing agent, so formulated as to produce the above-mentioned silicon content in the alloy.

Examples of suitable carbonaceous reducing agents are coal, coke, wood chips, and the lilre. A single carbonaceous reducing agent or a mixture of different reducing agents may be employed. The use of one or more reducing agents is primarily determined by the type and size of the manganiferous material used in the process. Thus, for example, wood chips are generally included when the material used is in a fine state of comminution. The selection of the carbonaceous reducing agent or agents is dictated by the desire of preventing a dense material and of obtaining a molten mass which is porous enough to easily allow the escape of gaseous substances formed during the smelting operation.

Examples of basic fiuxing agents suitable in practicing the invention are lime, magnesite, limestone, dolomite, and the like. The amount of fluxing agent employed is determined by the amount and composition of the gangue material in the manganese ore, and also by the degree of slag fluidity desired.

When the reduction process has reached completion, the resulting high-carbon intermediate alloy containing from about 2 to about 5 percent by weight of silicon is transferred to a desiliconizing vessel, which may be, for example, a ladle. Into this molten mass a powdered oxidizing agent, such as oxidic powdered manganiferous material, is blown by means of an oxygen-containing carrier gas. This carrier gas may be air, oxygenen riched air, or pure oxygen.

Powdered oxidic manganese is the preferred oxidizing agent because it may be employed partly as a fiuxing agent for desiliconizing the high-carbon intermediate alloy and partly as the source of manganese in the slag which may be recycled to the original smelting operation. The use of powdered manganese oxides is, therefore, highly advantageous from the standpoint of furnace efficiency and output.

The slag generated in the smelting furnace at the conclusion of the reduction operation contains less than about 7 percent manganese and is, therefore, disposable. The slag resulting from the desiliconizing operation contains about 47 percent by weight manganese as manganese oxide, if powdered oxide manganese is employed as the oxidizing agent. This manganese-rich slag is an excellent raw material for feeding to the smelting furnace along with manganese ore, and as such is recycled thereto for reempolyment.

The desiliconized high-carbon ferromanganese produced in the desiliconizing vessel has been found to have the following composition, in percent by weight: manganese, from about 74 to about 76 percent; carbon, about 5.5 percent; silicon, up to 1 percent, and the balance substantially iron and incidental impurities.

The production of a ferromanganese alloy having a carbon content of about 5.5 percent, instead of the usual 6.5 to 7 percent of commercially known alloys, renders the alloy of the present invention highly desirable to ferroalloy users.

To practice the present invention, a mixture consisting of manganese ore, recycled manganese-bearing slag, fluxing agent, and reducing agent may be prepared and charged to a single-phase, SOD-kilowatt submerged arc furnace. A suitable mixture has the following composition, in parts by weight.

Charge composition: Parts Manganese ore 63.4 Manganese slag 12.6 Fluxing agent 6.6

Reducing agent 17.4

Manganese ore (Weight percent on dry basis) Mn 44.88 Fe 6.32 Si 9.38 A1 0 6.18 CaO 1.16 MgO 1.16 BaO 1.16

Recycled manganese slag (percent):

Mn 49.95 Si0 26.40 A1 0 11.4 CaO 2.2 MgO 2.2 BaO 2.2 Metallics (FeMn) 11 Fluxing agent: Percent Dolomite (39% MgCO 58% CaCO 50 Limestone (98% CaCO 50 Reducing agent (pea coke):

C 89.7 Ash 8.2 Volatiles 2.1

Forty-eight and one half parts of high-silicon ferromanganese alloy are produced. This alloy and the disposable slag which is produced in the reduction operation have the following typical composition.

Intermediate alloy (percent):

The slag is discarded and the alloy is transferred to a desiliconizing ladle, into which 14.9 parts of comminuted manganese ore, suitably having the above-mentioned composition, are blown by a carrier gas consisting of 0.4 part of oxygen. This operation lasts until the silicon level of the alloy is reduced to, for example, 0.72 percent. One

l hundred and sixty pounds of manganese-bearing slag are obtained and held for recycling to a subsequent smelting and reducing operation. The compositions of the final high-carbon ferromanganese alloy are typically as follows.

Final alloy (percent) Mn 75.1 C 5.4 Si 0.72 Impurities 1.0 Fe Balance No substantial quantities of manganese are lost by volatilization. The recyclable slag has a manganese content of 49.95 percent and a composition substantially equal to the composition of the recycled slag employed in the reducing operation.

What is claimed is:

1. In a process for producing ferromanganese alloys by smelting in a metallurgical furnace a mixture of an oxidie manganese ore, a fiuxing agent, and a carbonaceous reducing agent, the improvement of which comprises efifecting said smelting in two steps, the first step comprising smelting a mixture of an oxidic manganese material, a lluxing agent, and a carbonaceous reducing agent to produce an intermediate ferromanganese alloy containing from about 2 to about 5 percent by Weight of silicon and a disposable slag; the second step comprising desiliconizing said intermedaite ferrornanganese alloy with oxidic manganese ore and gaseous oxygen to produce a ferromanganese alloy containing from about 74 to about 76 percent by Weight of manganese, from about 5 to about 6.5 percent by weight carbon, up to about 1 percent by weight silicon, and the balance substantially iron and incidental impurities, and a manganese-rich slag.

2. The process in accordance with claim 1, wherein the desiliconizing of the intermediate alloy is effected by adding to said intermediate alloy finely-divided oxidic manganese ore by means of an oxygen-containing gaseous carrier.

3. The process in accordance with claim 1, wherein the manganese-rich slag, obtained in the second step, is recycled ot the smelting operation for further processing.

References Cited in the file of this patent UNITED STATES PATENTS 2,128,615 Krus et a1 Aug. 30, 1938 FGREIGN PATENTS 545,169 Canada Aug. 20, 1957 OTHER REFERENCES Ser. No. 355,846, Perrin (A.P.C), published June 1 1943. 

1. IN A PROCESS FOR PRODUCING FERROMANGENESE ALLOYS BY SMELTING IN A METALLURGICAL FURANCE A MIXTURE OF AN OXIDIC MANGANESE ORE, A FLUXING AGENT, AND A CARBONACEOUS REDUCING AGENT, THE IMPROVEMENT OF WHICH COMPRISES EFFECTING SAID MELTING IN TWO STEPS, THE FIRST STEP COMPRISING SMELTING A MIXTURE OF AN OXIDIC MANGANESE MATERIAL, A FLUXING AGENT, AND A CARBONACEOUS REDUCING AGENT TO PRODUCE AN INTERMEDIATE FERROMANGANESE ALLOY CONTAINING FROM ABOUT 2 TO ABOUT 5 PERCENT BY WEIGHT OF SILICON AND A DISPOSABLE SLAG; THE SECOND STEP COMPRISING DWSILICONIZING SAID INTERMEDIATE FERROMANGENESE ALLOYS WITH OXIDIC MANGANESE ORE AND GASEOUS OXYGEN TO PRODUCE A FERROMANGANESE ALLOY CONTAINING FROM ABOUT 74 TO ABOUT 76 PERCENT BY WEIGHT OF MANGANESE, FROM ABOUT 5 TO ABOUT 6.5 PERCENT BY WEIGHT CARBON, UP TO ABOUT 1 PERCENT BY WEIGHT SILICON, AND THE BALANCE SUBSTANTIALLY IRON AND INCIDENTAL IMPURITIES, AND A MANGANESE-RICH SLAG. 